1. Field of the Invention
The present invention relates to a link-type front suspension device for a motorcycle.
2. Description of Background Art
U.S. Pat. No. 4,775,163 discloses a front link-type suspension for a motorcycle. The front link-type suspension has a pair of front forked portions extending on the right and left sides of a front wheel. Pivot links are provided having one-end rotatably mounted on the front forked portions and the other end for supporting an axle of the front wheel. Push rods include one-end rotatably mounted to intermediate portions of the pivot links and the other end connected to damping devices.
The above push rod is connected to a damper spring having an upper end connected to the vehicular body side and to a lower end of a damper. To be more specific, the push rod is rotatably mounted on the damper through a connecting arm in such a manner as not to be coaxial with the damper; and the push rod is directly connected to the damper spring not by way of a seat of the damper or the shaft but in such a manner as to be coaxial with the damper spring.
A front fender is supported by the push rod, to be thus moved together with the push rod.
The push rods are composed of a pair of right and left rod main bodies each extending substantially linearly and a push rod bracket for connecting the rod main bodies to each other. The push rod bracket serves as a portion to be connected to dampers or the like. In general, the rod main bodies and push rod bracket are separately formed and then welded to each other, or formed integrally with each other.
Incidentally, the lower end of the push rod is rotatably connected to the pivot link, and the upper end thereof is rotatably connected to the damper through the connecting arm and is directly connected to the seat of the damper spring. Further, the upper end of the damper is rotatably mounted on a top bridge and the upper end of the damper spring is fixed to the top bridge.
Accordingly, when the push rods are moved up and down by rocking motion of the pivot links caused by vertical motion of a front end, the upper ends of the push rods connected to the dampers and damper springs are liable to be irregularly moved in the longitudinal direction, so that the push rods are applied to bending. This decreases the operability, and also increases the weight because of the need of the increased bending strength, leading to the increased unsprung weight. Accordingly, an object of the present invention is to provide push rods that are excellent in operability.
In the case where the front fender is supported by the push rods and is moved together therewith, since the front fender is not moved with a stroke corresponding to that of the front wheel which is moved up and down, it is required to preset a sufficient clearance between the front wheel and the front fender. Accordingly, another object of the present invention is to reduce such a clearance.
In the case where the rod main bodies and push rod bracket constituting the push rods are separately formed and then welded to each other, these components are generally formed from the same material. In this case, if the components are formed from iron, the total weight thereof is increased, and if they are formed from a light alloy such as an aluminum alloy, the material cost thereof is increased. Further, if the components are formed integrally with each other, it takes a lot of labor to finish them. Accordingly, a further object of the present invention is to provide push rods having a structure advantageous in manufacture thereof
The above front suspension is configured that a top bridge for mounting the front forked portions serves as a member for receiving a load applied to the dampers. While not clearly described in the above document, such a top bridge is generally connected to an upper end of a stem pipe passing through a head pipe of a body frame, and accordingly, upper ends of the damping devices as well as the upper ends of the front forked portions are mounted to the vehicular side by means of the common top bridge.
A structure wherein the top bridge receives a load of the damping devices has a problem in that the top bridge must have a high rigidity for withstanding a large load of the damping devices, and thereby it must be enlarged in size and increased in weight. Another problem is that since the damping devices, front forked portions and stem pipe are supported only by one top bridge, the top bridge is connected to all of the above components and must be removed as a whole for exchanging one of the above components, thereby decreasing the maintenance characteristic.
While similarly not clearly described in the above document, the front forked portions and stem pipe are generally mounted on the top bridge by previously providing, in the top bridge, right and left front forked portion mounting holes and a central stem pipe mounting hole located behind the front forked portion mounting holes. The top bridge, from top to bottom, is mounted to the front forked portions and the stem pipe in such a manner that the upper ends of the front forked portions and the upper end of the stem pipe respectively pass through the front forked portion mounting holes and the stem pipe mounting hole. The top bridge is fixed to the front forked portions and the stem pipe by clamping the front forked portion mounting holes with slits after insertion of the front forked portions in the front forked portion mounting holes and fastening a portion of the stem pipe projecting from the stem pipe mounting hole with a nut.
In the case of the adoption of a slant type in which a stem pipe is slanted with respect to each front forked portion, there occurs a problem in that it is impossible to sequentially assemble parts in the order from bottom to top (for example, to mount a steering stem at intermediate portions of the front forked portions) and to finally mount the top bridge. In other words, the steering stem and top bridge must be fastened prior to mounting of the top bridge, to thereby complicate the assembling procedure.
A portion, mounted on the top bridge side, of the damper is generally elastically supported by a rubber bushing or an annular bushing. However, in this case, since the annular rubber member is used with its circular face located in the horizontal direction, the rubber member has a reduced rubber volume and keeps up with only a motion in the rotational direction. Also, while a thrusting side of the rubber member requires a rubber volume larger than that of the extension side of the rubber member, it is impossible to provide a rubber volume and hardness suitable for the required characteristics to each of the thrusting side and the extension side of the rubber member.